Generally, a clock signal includes a signal used to coordinate the actions of two or more circuits. Frequently, a clock signal oscillates between a high and a low state, normally with a 50% duty cycle, and is usually in the form of a square wave. A clock distribution network, generally, distributes the clock signal(s) from a common point to all the elements or components that need or make use it. Since this distribution function is often vital to the operation of a synchronous system or circuit, much attention has been given to the characteristics of these clock signals and the electrical networks used in their distribution.
Clock signals are typically operate at the highest speeds of any signal, either control or data, within the entire synchronous system and, due to the clock's wide usage, typically also includes the greatest capacitive loading and signal fan-out. Since data signals are often provided with a temporal reference in the form of the clock signal, the clock signal's waveform must frequently be particularly clean and sharp.
One of the measures of clock, or waveform in general, consistency and control is jitter. Jitter is frequently an unwanted variation of one or more characteristics of a periodic signal in electronics and telecommunications. Jitter may be seen in characteristics such as the interval between successive pulses, or the amplitude, frequency, or phase of successive cycles. For clock jitter, there are three commonly used metrics: absolute jitter, period jitter, and cycle to cycle jitter. Cycle to cycle jitter is generally the difference in length of any two adjacent clock periods. Although, it is understood that the above is merely one illustrative example to which the disclosed subject matter is not limited.